This invention relates to a paper feed mechanism for multiple copy printers and, more particularly, to high-speed impact printers, teleprinters, and similar equipment used in data processing systems.
In such printers, a continuous paper web having rows of perforations along its edges is commonly employed as the print-receiving member. The advancement, or slewing, of the paper web is provided by sprocket tractors which engage the perforations at the edge of the web.
The tractors are intermittently actuated by escapement devices or, preferably, by stepping motors or low inertia motors, to provide on command, the advancement of the web after each printing of a line has been completed. In order to assure that proper paper web tension is provided proximate the print line, two pairs of tractors are usually used, one pair being placed upstream of the print line and the other downstream.
In these printers, a platen, in the form of a freely rotating cylinder, is aligned in correspondence with the print line. Therefore, instead of the tractor configuration described above, in another type of feed mechanism, the web is wrapped about the platen through an arc of approximately 180.degree. and a single pair of tractors engages the web perforations both upstream and downstream of the platen.
However, in paper feed mechanisms of this latter type, if the print-receiving member consists of multiple copies, a relative shift occurs among the individual sheets of paper which form the web. This shift is particularly pronounced with respect to the sheet in contact with the platen. Consequently, in the region of the downstream tractor (relative to the direction of advancement of the web), the sprocket holes frequently tear, thereby resulting in clogging of the feed mechanism and an extremely irregular advancement of the web.
Accordingly, it is the object of the instant invention to obviate the aforementioned disadvantages of the prior art paper feed mechanisms.
Another object of the instant invention is to provide a paper feed mechanism for a printer used in data processing systems which is reliable, inexpensive, and consistent in performance.
Another object of the instant invention is to provide a reliable and inexpensive printer paper feed mechanism for use with multiple copy print-receiving members.